US6641698B2 - Integrated circuit fabrication dual plasma process with separate introduction of different gases into gas flow - Google Patents

Abstract

A dual plasma process generates a microwave neutral plasma remote from a semiconductor wafer and a radio frequency (RF) ionized plasma adjacent to the wafer for simultaneous application to the wafer. A first gas flows through a microwave plasma generation area, without a second gas in the gas flow, to generate the neutral microwave plasma. The second gas is added to the gas flow downstream of the microwave plasma generation area prior to an RF plasma generation area.

Description

CROSS-REFERENCE TO RELATED INVENTIONS

This invention is a division of U.S. application Ser. No. 09/747,638, filed Dec. 22, 2000, now U.S. Pat. No. 6,461,972 B1.

FIELD OF THE INVENTION

This invention relates to semiconductor wafer processing in the fabrication of integrated circuits. More particularly, the present invention relates to a new and improved way to combine a microwave generated neutral species plasma with a radio frequency generated ionized species plasma for dual plasma fabrication processes. As a result, the useful lifetime of the hardware is increased, the generation of unwanted particles from the hardware is reduced, the mean time between maintenance is increased, the stability and integrity of the performance of the etch or clean process is increased, and the overall cost of the process is decreased.

BACKGROUND OF THE INVENTION

In the fabrication of integrated circuits (IC's) on semiconductor wafers, “dual” plasma processes have been developed to etch dielectric, polysilicon and metal materials from the wafers. Dual plasma processes have also been used to remove organic materials, including photoresist, BARC (bottom anti-reflection coating) layers, etc., from the wafers. Either plasma can be generated alone and applied to the wafer in a “single plasma mode.” The dual plasma mode, however, enables a greater variety of resist and residue cleaning applications than does the single plasma mode.

In the dual plasma mode, two plasmas are applied to a wafer to realize the etch process requirements or parameters. Such process requirements and parameters involve the process rate, the uniformity of the process across the entire wafer, the selectivity of the process to the type of material to be removed and the shape, profile and aspect ratio of the features on the wafer, among other parameters and requirements. One plasma is typically generated by microwave energy, and the other plasma is typically generated by radio frequency (RF) energy.

Typically, one plasma is generated in a region remote from the wafer to avoid damage caused by uncontrolled ion bombardment from the plasma. Typically, the remotely generated plasma is the microwave plasma, or an “inductively coupled plasma” (ICP). The microwave plasma generation area is far enough removed from the wafer that any ions generated in the microwave plasma recombine or are removed, so that only neutral species (e.g. atomic oxygen, atomic hydrogen, etc.) from the microwave plasma reach the wafer. The neutral species are plasma components without an electrical charge. Some of the neutral species are also typically generated in the plasma as a result of decomposition of the original gaseous molecules.

Without ions, the neutral species involve only chemically reactions in the material removal process. The reaction rate depends on the specie type, the material type and the temperature in the process chamber.

For advanced resist and residue removal applications, an additional RF plasma is introduced independently of the microwave plasma near the wafer by applying RF power to the chuck. The RF plasma includes charged reactive ionized species (ions). The ionized species affect the surface of the wafer with high energy (i.e. impact the wafer with a “bombardment” effect) and with a reactivity that can be higher than the reactivity of the neutral species. The ion species improve the efficiency of the process, so that highly modified resist materials and tough residues can be removed by the dual plasma mode.

The dual plasma mode is based on introducing fluorine and non-fluorine process gases into the process chamber through the microwave plasma generation area. The gases that contain fluorine include carbon tetrafluoride (CF4), fluoroform (CHF3), hexafluoroethane (C2F6), nitrogen trifluoride (NF3) and sulfur hexafluoride (SF6), among others. The non-fluorine gases include oxygen, nitrogen, carbon monoxide and water vapor, among others. The gases are mixed together and the gas mixture flows through the remote microwave plasma generation area. The microwave plasma is generated with non-charged reactive neutral species, such as atomic fluorine (F), atomic oxygen (O), atomic nitrogen (N), atomic hydrogen (H), etc. The neutral species can reach the RF plasma generation area near the wafer. In the RF plasma generation area, the RF plasma (including the charged reactive ionized species) is formed in the gas mixture. The combination of both plasmas forms the plasma environment that removes the resist materials and residues that remain on the wafer surface after performing other fabrication processes, such as wafer etch, implantation, etc.

An exemplaryprior art assembly100 for a chamber configuration for a dual plasma process is shown in FIG.1. Theassembly100 includes awafer processing chamber102 connected to a microwaveplasma generation assembly104. The gas mixture (e.g. containing both the fluorine and non-fluorine gases) flows through the microwaveplasma generation assembly104, into thechamber102, down to awafer106 and out of the chamber through agas outlet108. Thewafer106 is thus subjected to both of the plasmas inside thechamber102.

Themicrowave plasma assembly104 includes aplasma tube110 surrounded by a microwave waveguide112 that is connected to amicrowave power source114. Theplasma tube110 is typically made of quartz, sapphire, ceramic alumina or other dielectric materials. A microwaveplasma generation area115 is inside theplasma tube110. The gas mixture enters theplasma tube110 through agas inlet116. As the gas mixture flows through theplasma tube110, themicrowave power source114 supplies microwave power to the microwave guide112, which generates the microwave plasma in the gas mixture in theplasma tube110. The gas mixture (e.g. the microwave plasma of neutral species, including the neutral fluorine reactive species) flows from theplasma tube110 into thechamber102 through achamber inlet118.

Thechamber102 includes agas distribution module120, an RFplasma generation area122 and awafer chuck124. Thewafer106 sits on thewafer chuck124. Thewafer chuck124 is connected to anRF power source126. TheRF power source126 supplies RF power to thewafer chuck124, which generates the RF plasma in the RFplasma generation area122 directly above thewafer106. As the gas mixture enters thechamber102, the gas mixture flows around and through thegas distribution module120, which evenly distributes the gas mixture across thewafer106 and the RFplasma generation area122. As the gas mixture approaches thewafer106, ions (e.g. fluorine ions, oxygen ions, etc.) are generated in the RF plasma in the RFplasma generation area122. Thewafer chuck124 is RF biased by the RF power from theRF power source126, so the ions are accelerated toward thewafer106 to bombard thewafer106. The ionized and neutral species of the two plasmas, thus, perform the etch, ash or clean process on thewafer106.

In many cases, the presence of the fluorine gas in theplasma tube110 can modify or damage theplasma tube110 and other parts in theassembly100 that are close to the microwave plasma generation area by eroding the inner wall of theplasma tube110 or parts of thechamber102 or decomposing the surface of the inner wall of theplasma tube110 or the parts of thechamber102. The damage affects the overall process, reduces the useful lifetime of the hardware, causes unwanted particle generation from the damaged areas, reduces mean time between maintenance and increases the cost of the process, among other things. When the inner wall of theplasma tube110 or any parts of thechamber102 are eroded, particles from the inner wall enter the gas mixture flow. Such particles can damage thewafer106 or alter structures (not shown) formed on thewafer106. The erosion also reduces the useful lifetime of the hardware, since the eroded hardware has to be replaced. Frequent interruptions in the fabrication of the IC's in order to perform maintenance to replace hardware (i.e. short mean time between maintenance) increases the cost of the fabrication process and reduces the number of IC's that can be fabricated in a given time period.

It is with respect to these and other background considerations that the present invention has evolved.

SUMMARY OF THE INVENTION

The present invention decreases the overall cost of dual plasma etch, ash and clean processes performed on semiconductor wafers, increases the useful lifetime of the hardware used in the processes, reduces the generation of unwanted particles from the hardware, increases the mean time between maintenance and increases the stability and integrity of the performance of the plasma processes. A gas flow of only non-fluorine gas passes through the microwave plasma generation area that is remotely located from the wafer. Fluorine gas is introduced into the gas flow downstream of the microwave plasma generation area, instead of upstream, so the fluorine gas does not pass through the microwave plasma generation area. In this manner, the risk of damage by fluorine to the plasma tube in which the microwave plasma is generated and to surrounding structures is eliminated. Since no erosion occurs to the hardware by the fluorine gas, significantly fewer particles that could damage the wafer or reduce the stability or integrity of the plasma process are introduced into the gas flow, and the useful lifetime of the hardware is greatly increased. Thus, the plasma process can operate longer without having to be shut down as often for maintenance purposes as is necessitated by prior dual plasma processes, so the mean time between maintenance increases. The longer operating time increases the average number of wafers that can be processed in a given time period. The increased number of processed wafers and the decreased frequency of replacing hardware decreases the overall cost per wafer of the plasma process.

These and other improvements are achieved by performing a dual plasma process, such as a plasma etch and/or clean process, on a semiconductor wafer by flowing the first gas through the first plasma generation area to generate the first plasma without the second gas. After the first gas passes through the first plasma generation area, the second gas is added to the gas flow of the first gas. The combined gases, containing the second gas and the plasma of the first gas, are flowed through the second plasma generation area to generate the second plasma from the gas mixture. Both plasmas are then applied simultaneously to the semiconductor wafer.

The first gas is preferably a non-fluorine gas, and the first plasma is preferably generated therefrom with microwave energy. The second gas is preferably a fluorine gas, and the second plasma is preferably generated from the gas mixture with radio frequency energy.

The gas flow preferably passes through a distribution system having several nozzles that evenly distribute the gases to the second plasma generation area next to the wafer. Thus, in one embodiment, the gases are preferably mixed together upstream of the nozzles and pass through the same nozzles together. In another embodiment, the gases are preferably mixed together downstream of the nozzles, in which case, the gases preferably flow through different paths to different sets of the nozzles to be separately distributed to the second plasma generation area and mixed together upon exiting from the nozzles.

The previously mentioned and other improvements are also achieved in an improved dual plasma process assembly in which a semiconductor wafer is subjected to a dual plasma process, such as a plasma etch and/or clean process. The improved dual plasma process assembly includes a gas flow path and a gas mixture area. The gas flow path extends from the first plasma generation area, through the second plasma generation area, to the wafer. The gas mixture area is in the gas flow path between the two plasma generation areas. The first gas (preferably a non-fluorine gas), from which the first plasma is generated (preferably by microwave energy), enters the gas flow path at the first plasma generation area. The second gas (preferably a fluorine gas) enters the gas flow path at the gas mixture area, downstream of the first plasma generation area. Thus, the second gas does not flow through the first plasma generation area. The second plasma is generated (preferably by radio frequency energy) from the gas mixture of the second gas and the first gas containing the first plasma.

The assembly also preferably includes distribution nozzles between the two plasma generation areas for evenly distributing the gases to the second plasma generation area next to the wafer. In a first embodiment, the two gases are preferably mixed upstream of the nozzles and flow together through the same nozzles. In a second embodiment, one portion of the nozzles preferably receives the first gas/plasma and evenly distributes it to the second plasma generation area, and a second portion of the nozzles receives the second gas and evenly distributes it to the second plasma generation area. In this case, the gases are mixed downstream of the nozzles upon exiting from the nozzles.

A more complete appreciation of the present invention and its scope, and the manner in which it achieves the above noted improvements, can be obtained by reference to the following detailed description of presently preferred embodiments of the invention taken in connection with the accompanying drawings, which are briefly summarized below, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a prior art dual plasma process assembly.

FIG. 2 is a cross sectional view of a dual plasma process assembly incorporating the present invention.

FIG. 3 is a cross sectional view of a dual plasma process assembly incorporating the present invention in an alternative embodiment to the dual plasma process assembly shown in FIG.2.

FIG. 4 is a cross sectional view of a gas distribution assembly utilized in the dual plasma process assembly shown in FIG.3.

DETAILED DESCRIPTION

A dualplasma process assembly130 generally includes aprocess chamber132 and amicrowave plasma assembly134, as shown in FIG.2. In the fabrication of integrated circuits (ICs) (not shown) on semiconductor wafers (e.g. wafer136) such dual plasma processes commonly include etch, ash and clean processes that remove material, residue or debris from the surface of thewafer136. The dual plasma mode, or process, typically generates two plasmas, which are applied to thewafer136 simultaneously, to perform the dual plasma process on thewafer136. The two plasmas typically include a microwave neutral (not electrically charged) reactive species plasma generated in a microwaveplasma generation area138 in themicrowave plasma assembly134 remote from thewafer136 and a radio frequency (RF) reactive ionized (electrically charged) species plasma generated in an RFplasma generation area140 in theprocess chamber132 next to thewafer136.

The microwave plasma is typically generated from a gas that does not contain fluorine (or chlorine). The RF plasma, on the other hand, is typically generated from a mixture of the non-fluorine gas (after the microwave plasma has been generated therein) and a gas that contains fluorine (or chlorine). The non-fluorine gas flows, without the fluorine gas, through the microwaveplasma generation area138, so that the microwave plasma can be generated from the non-fluorine gas. The fluorine gas is then added to the flow of the non-fluorine gas (containing the non-fluorine microwave plasma) downstream of the microwaveplasma generation area138, instead of upstream. In this manner, any potential damage that might be caused by the presence of the fluorine gas in the microwaveplasma generation area138 is eliminated.

Themicrowave plasma assembly134 typically includes a conventionalmicrowave power source142, a conventional microwave guide144 and a conventional plasma tube146. The plasma tube146 is typically made of quartz, sapphire, ceramic alumina or other dielectric materials. Aconventional source148 for the non-fluorine gas is connected to aninlet150 of the plasma tube146 to deliver the non-fluorine gas into the plasma tube146. The microwaveplasma generation area138 is inside the plasma tube146. Themicrowave power source142 is connected to the microwave guide144 to deliver microwave power thereto. The plasma tube146 is surrounded by the microwave guide144, so that microwave energy generated by the microwave power in the microwave guide144 is delivered to the non-fluorine gas flowing through the microwaveplasma generation area138. The microwave plasma is, thus, generated from the microwave energy and the non-fluorine gas.

The plasma tube146 connects to theprocess chamber132, so that the microwave plasma can flow through anoutlet152 in the plasma tube146 into theprocess chamber132. Themicrowave plasma assembly134 is typically external to theprocess chamber132, so that the microwaveplasma generation area138 is sufficiently remote from thewafer136 that any ions generated by themicrowave plasma assembly134 in the microwave plasma do not reach thewafer136 to cause ion bombardment on thewafer136. Therefore, only neutral (i.e. not electrically charged) components, or species, of the microwave plasma reach thewafer136.

Theprocess chamber132 generally includes a conventionalconductive wafer chuck154, a conventionalgas distribution assembly156 and agas mixing chamber158. Thewafer136, upon which the dual plasma process is to be performed, is placed on thewafer chuck154 inside theprocess chamber132 through an access door (not shown) in asidewall160 of theprocess chamber132 by a robot arm (not shown). The RFplasma generation area140 is adjacent to and directly above thewafer136. Thegas distribution assembly156 includes a gas distribution “shower head-like”device162 with a set ofdistribution nozzles164 and adistribution cone166 above the RFplasma generation area140. Theshower head162 connects to thegas mixing chamber158, so that thedistribution nozzles164 are open to thegas mixing chamber158. Thegas mixing chamber158 connects through agas duct168 to theoutlet152 of the plasma tube146 and through anothergas duct170 to asource172 of the fluorine gas external to theprocess chamber132.

The non-fluorine gas containing the microwave plasma flows through thegas duct168 into thegas mixing chamber158. The fluorine gas flows from thefluorine gas source172 through thegas duct170 into thegas mixing chamber158. The fluorine gas and the non-fluorine gas mix together in the mixingchamber158 to create a gas mixture. The gas mixture flows through thedistribution nozzles164 in theshower head162 and is evenly distributed by thedistribution cone166 to the RFplasma generation area140 next to thewafer136.

Thewafer chuck154 is electrically connected to an RF power source174 (typically external to the process chamber132). TheRF power source174 delivers RF power to thewafer chuck154 to RF bias thewafer chuck154, which thereby delivers RF energy to the RFplasma generation area140. The RF energy generates the RF plasma in the gas mixture containing the fluorine gas in the RFplasma generation area140. The RF plasma is a reactive ion plasma (i.e. contains electrically charged species). The RF power causes an RF bias of thewafer chuck154, which accelerates the fluorine and other ions in the RF plasma toward thewafer136 to cause ion bombardment on thewafer136. At the same time, the neutral species in the accompanying microwave plasma also contact thewafer136. The reactive ionized species and the reactive neutral species remove unwanted materials (e.g. films, residue, debris, etc.) from the surface of thewafer136. The gas mixture, along with removed material from thewafer136, flows around thewafer chuck154 and out agas exhaust vent176 from theprocess chamber132.

An alternative dualplasma process assembly178, as shown in FIG. 3, includes themicrowave plasma assembly134 and aprocess chamber180. Themicrowave plasma assembly134 is similar to thesame assembly134 shown in FIG.2. Theprocess chamber180, on the other hand, includes certain differences from theprocess chamber132 shown in FIG.2. In particular, theprocess chamber180 includes agas distribution assembly182 that receives the fluorine and non-fluorine gases through different gas flow paths, so that the fluorine and non-fluorine gases do not mix until exiting from thegas distribution assembly182 into the RFplasma generation area140.

Thegas distribution assembly182 includes adistribution cone184 and ashower head186. Theshower head186 is shown in greater detail in FIG.4 and includes two sets ofnozzles188 and190. The tops of thenozzles188 open to the interior of thedistribution cone184. The tops of thenozzles190, however, open to achannel192 within theshower head186 that connects to agas duct194. The bottoms of all of thenozzles188 and190 open to the RF plasma generation area140 (FIG.3). Thenozzles188 and190 are evenly spaced, so that the non-fluorine gas (containing the microwave plasma) and the fluorine gas are evenly distributed to the RFplasma generation area140. Upon exiting from thenozzles188 and190 into the RFplasma generation area140, the two gases mix together.

Referring back to FIG. 3, thegas duct194 connects to thefluorine gas source172. Thus, the fluorine gas flows into theshower head186 from thegas duct194 and through the channel192 (FIG. 4) and the nozzles190 (FIG. 4) into the RFplasma generation area140.

The top of thedistribution cone184 connects to apre-distribution chamber196. Thepre-distribution chamber196 in turn connects to thegas duct168, which connects to themicrowave plasma assembly134 at theoutlet152.

The non-fluorine gas enters the dualplasma process assembly178 at theinlet150 to the plasma tube146. Powered by themicrowave power source142, the microwave guide144 generates the microwave plasma in the non-fluorine gas in the microwaveplasma generation area138 in the plasma tube146. The non-fluorine gas (containing the microwave plasma) flows out of the plasma tube146 through theoutlet152 into thegas duct168 in theprocess chamber180. The non-fluorine gas flows through thegas duct168 into thepre-distribution chamber196 and to thedistribution cone184. The non-fluorine gas then flows through the nozzles188 (FIG. 4) in theshower head186 and into the RFplasma generation area140.

Upon entering the RFplasma generation area140, the RFbiased wafer chuck154 generates the RF plasma in the gas mixture containing fluorine gas. The fluorine and other ions in the RF plasma then bombard the surface of thewafer136. The neutral species of the microwave plasma in the non-fluorine gas flow also contact the surface of thewafer136. Together, the RF plasma and the microwave plasma perform the dual plasma process on thewafer136.

In both embodiments (FIGS.2 and3), the microwave plasma is introduced into theprocess chamber132 or180 from the side. However, the microwave plasma may also be introduced into theprocess chamber132 or180 from the top, which results in different process parameters.

In either the embodiment shown in FIG. 2 or the alternative embodiment shown in FIG. 3, the fluorine gas is added to the flow of the non-fluorine gas downstream of the microwaveplasma generation area138. Thus, the present invention has the advantage of eliminating any damage by the fluorine gas or fluorine plasma to the plasma tube146 and any surrounding structure, such as thegas duct168. In this manner, the useful life of the hardware (in particular the plasma tube146) and the time between maintenance periods are greatly extended. Also, the stability and integrity of the dual plasma process in increased, since fewer foreign particles are introduced into the gas flow by erosion of the hardware. Thereby, the over all cost of the dual plasma process is decreased.

In the case of the embodiment shown in FIG. 3, theshower head186 is more complex and expensive than the shower head162 (FIG.2). The introduction of the fluorine gas into the gas flow even further downstream from the microwaveplasma generation area138 than in the embodiment shown in FIG. 2, however, may justify the added expense, depending on the specific situation in which the dual plasma process assembly130 (FIG. 2) or178 (FIG. 3) is used.

Additionally, due to the less damaging nature of the non-fluorine gas in the plasma tube146, a plasma tube146 made of quartz is preferably used, instead of the more expensive, but more durable, sapphire plasma tube, without sacrificing the performance of the overall dual plasma process. Thus, the equipment cost is reduced.

Presently preferred embodiments of the invention and its improvements have been described with a degree of particularity. This description has been made by way of preferred example. It should be understood that the scope of the present invention is defined by the following claims, and should not be unnecessarily limited by the detailed description of the preferred embodiments set forth above.

Claims (14)

The invention claimed is:

1. Apparatus for subjecting a semiconductor wafer simultaneously to first and second plasmas during processing of the wafer, comprising:

a process chamber within which to support a semiconductor wafer and apply the first and second plasmas simultaneously to the semiconductor wafer during processing;

a source of non-fluorine gas;

structure defining a first plasma generation area at a location outside of the process chamber, the first plasma generation area defining structure connected to receive non-fluorine gas supplied from the non-fluorine gas source;

a first plasma generator associated with the first plasma generation area defining structure and operative to generate a first plasma within the non-fluorine gas within the first plasma generation area;

a source of fluorine gas;

structure defining a gas mixture area which is separated from the first plasma generation area, the gas mixture area defining structure connected to receive the non-fluorine gas containing the first plasma from the first plasma generation area and also connected to receive the fluorine gas supplied from the fluorine gas source, the gas mixture area defining structure creating a mixture of the fluorine gas and the non-fluorine gas containing the first plasma;

structure within the process chamber defining a second plasma generation area

the second plasma generation area

defining structure connected to receive the mixture of the fluorine gas and the non-fluorine gas from the gas mixture area;

a second plasma generator associated with the second plasma generation area for generating a second plasma within the fluorine gas of the mixture of the fluorine gas and the non-fluorine gas containing the first plasma. and

structure within the process chamber for supporting the semiconductor wafer relative to the second plasma generation area defining structure to simultaneously contact the semiconductor wafer with the first plasma and the second plasma.

2. Apparatus as defined inclaim 1 wherein the dual plasma etches and clean the semiconductor wafer.

3. Apparatus as defined inclaim 1 further comprising:

a plurality of distribution nozzles disposed between the first and second plasma generation areas defining structures and operative to flow the fluorine and non-fluorine gas therefrom; and wherein:

the gas mixture area is defining area connected upstream of the flow of fluorine and non-fluorine gas from the distribution nozzles.

4. Apparatus as defined inclaim 1 further comprising:

a plurality of distribution nozzles disposed between the first and second plasma generation areas defining structures and operative to flow the fluorine and non-fluorine gas therefrom; and wherein:

the gas mixture area defining area is connected downstream of the flow of fluorine and non-fluorine gas from the distribution nozzles.

5. Apparatus as defined inclaim 4, wherein:

a first portion of the distribution nozzles connects to the first plasma generation area defining structure;

a second portion of the distribution nozzles connects to the source of fluorine gas;

the first plasma flows through the first portion of the distribution nozzles;

the fluorine gas flows through the second portion of the distribution nozzles; and

the fluorine gas and the first plasma mix together upon exiting from the distribution nozzles.

6. Apparatus as defined inclaim 1, wherein:

the first plasma generator is a microwave energy source.

7. Apparatus as defined inclaim 6, wherein:

the gas mixture area defining structure is remote from the microwave energy source.

8. Apparatus as defined inclaim 7, wherein:

the second plasma generator is a radio frequency energy source.

9. Apparatus as defined inclaim 1, wherein:

the non-fluorine gas is selected from the group consisting of oxygen, nitrogen, argon, carbon monoxide and water.

10. Apparatus as defined inclaim 1, wherein:

the fluorine gas is selected from the group consisting of carbon tetrafluoride, fluoroform, hexafluoroethane, nitrogen trifluoride and sulfur hexafluoride.

11. Apparatus as defined inclaim 1, wherein:

the second plasma generation area defining structure is within the process chamber.

12. Apparatus as defined inclaim 1, further comprising:

a plurality of distribution nozzles within the process chamber to receive and disribute the non-fluorine gas containing the first plasma.

13. Apparatus as defined inclaim 12, wherein:

the plurality of distribution nozzles also receives and distributes the fluorine gas.

14. Apparatus as defined inclaim 13, wherein:

the plurality of distribution nozzles include a first portion and a second portion;

the first portion of the distribution nozzles receives and distributes the non-fluorine gas containing the first plasma; and

the second portion of the distribution nozzles receives and distributes the fluorine gas.

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